MTN - OUTRAGEOUS BILLING

In October 2022, I was due for an upgrade. I upgraded a laptop which returned within the stipulated time. It was only credited 6th April 2023. My MTN account is in arrears since November 2022 as I refuse to pay for a laptop that I have returned. I log into the MTN app and it shows Total Outstanding amount R11719.85, how is that even possible? Outraged. I tried to call MTN and was told account is suspended so cannot reach the customer care. I have emailed customercare, I cannot wait to hear this excuse. I have always been a good customer and my account has never been in arrears.